Formal weaning studies must be performed to assess the heart’s ability to maintain the circulation without VA ECMO support. Circuit flows must be reduced to assess native heart function in the setting of an increased venous return. Flow is reduced in a series of steps while haemodynamic and echocardiographic (TTE or TOE) data are collected according to the echo Weaning Form.
As prolonged VA ECMO therapy is associated with complications, a decision about weaning should occur as soon as feasible. Generally, this is determined by the original pathology, the level of ECMO support, the haemodynamic stability and inotropic support. (See prerequisites in the echocardiographic weaning).
The ability to wean off VA ECMO takes multiple factors into account including the haemodynamic robustness of the patient, urgency for decannulation, the likelihood of further recovery and echocardiographic findings. The echo plays the central role in the decision-making process and is described in detail below.
Echocardiographic weaning protocol
Prior to commencing a ‘weaning study’, the following prerequisites should be met. However, in the event of progressive ECMO complications (such as significant bleeding or cannula related sepsis), a weaning study may be performed earlier.
Most quantitative measures aid as a marker of stability and likely successful wean, however, they are not absolute.
Prerequisites for weaning
- Treating team and intensivist agree on the appropriateness of a weaning study (i.e. a successful weaning study will precipitate a change in the patient’s management, such as decannulation)
- Patient is on the “bridge to recovery” pathway (i.e. not currentlydefinitely being palliated, or on the “ECMO to VAD” pathway or on a “palliation” pathway)
- Haemodynamic stability
- Stable ECMO flow (ideally <3 L/min) & on <3 L/min fresh gas flow
- Consistent arterial pulsatility >24 hours and Pulse pressure >20 mmHg
- MAP >60 mmHg in the absence or with low doses of inotrope/vasopressors
- Noradrenaline <10 mcg/min
- Adrenaline <5 mcg/min, milrinone <20 mcg/min
- Stable cardiac rhythm (preferably sinus rhythm)
- Stable metabolic state
- Pulmonary function should not be severely impaired
- Minimal pulmonary infiltrates on chest X-ray
- No evolving organ dysfunction
- Underlying pathology has had an appropriate time for recovery
- Formal echocardiography examination suggestive of improvement of cardiac function
- Theatre availability
- A treatment plan thatparticularly addressessing limits of therapy or full ECLS if required afterpost decannulation should be discussed and documented pre cannulation
Due to the heparin-bonded circuit and the transient nature of the weaning study, therapeutic anticoagulation is not required for the purpose of the study.
The weaning process consists of reducing the amount of ECMO support while closely monitoring the patient’s haemodynamics and echocardiographic measurements. This reduction in ECMO support leads to changes in the loading conditions of the heart, which includes an increase in preload of the heart and a decrease in systemic afterload. When the heart is ready to be weaned off ECMO, the cardiac output will remain stable or even augment, without developing any new signs of heart failure.
The echocardiographic examination is preferably performed using transthoracic echocardiography (TTE). In the event of inadequate TTE imaging, transoesophageal echocardiography (TOE) may be used to supplement the TTE study. Obtaining consent from the patient or the medical treatment and decision maker (MTDM) is necessary before performing a TOE (See Guideline: Prevention and management of transoesophageal echo related complications).
Haemodynamics should be monitored at baseline (i.e. prior to a reduction in ECMO support) and at each level of reduced ECMO flow. These parameters should be documented on the standardised ECMO weaning form.
The following echocardiographic parameters should be collected
- LV size
- LVED diameter (parasternal long-axis view)
- RV size
- RVED diameter – midlevel (RV-focused apical four-chamber view)
- LVEF (Visual, Simpson’s method or 3D)
- Consider echo contrast if poor TTE LV wall definition
- LVOT VTI
- Each measurement should be taken from the same position. To achieve this, the echocardiographer should zoom in on the LVOT, add colour to identify the middle of the LVOT, and therefore laminar flow, place the pulse wave in the outflow tract close to the aortic valve so that the spectral phase consistently shows a closing click without an opening click
- The VTI is then measured by tracing the instantaneous dense modal velocities throughout systole.
- Average 3 beats in sinus rhythm and 5 in atrial fibrillation.
- TDSa (lateral mitral annulus peak systolic velocity)
- RV S’
- RVOT VTI
Severity of mitral/tricuspid/aortic regurgitation
Size of pericardial collection
ECMO flow reduction
A sequential reduction in ECMO flow is necessary to increase the loading conditions of the heart, followed by a thorough assessment of the heart under these increased loading conditions (via echocardiography and haemodynamic assessment).
Reduce ECMO flow by 1 L/min and assess for 5-10 minutes at each new flow rate. If stability is maintained at each level, continue to reduce until at 1 L/min. A final assessment should be made at no lower than 0.5 L/min flow  (e.g. 3 ® 2 ® 1 ® 0.5 L/min). Extended periods (i.e. more than 5 minutes) at 0.5 L/min should be avoided except in exceptional circumstances. At 0.5 L/min, only the LVEF, LVOT VTI & TDSa need to be assessed.
Definition of successful VA ECMO weaning
There is not one parameter that predicts a successful wean, and the clinician should always use a combination of qualitative and quantitative measures to help predict whether a patient can safely be liberated from ECMO. The following parameters are associated with a likely success, although it is acknowledged that not all parameters may be measurable in every case:
No significant change in haemodynamic parameters at the time of weaning
- A fall in MAP below 55 mmHg or a fall of greater than 20 mmHg with ECMO blood flow reduction is considered clinically significant
- A rise in CVP (or MPAP – if predominately LVF) of greater than 5 mmHg or to a value greater than 15 mmHg (35 mmHg for MPAP) is considered significant
No significant increase in noradrenaline or adrenaline during the study
- Inotrope doses prior to the weaning study should be set to levels expected to be required following decannulation (typically adrenaline equivalent dose of 0-10 µg/min).
- A rise of noradrenaline for hypotension (see above) of more than 2 µg/min during the weaning phase is considered significant.
At minimum ECMO flow support 
- LVEF >20-25%
- LVOT VTI ≥10 cm
- TDSa ≥6 cm/s
Recruitment of LV and / or RV function (qualitatively or quantitatively) 
Absence of significant LV dilatation 
No abnormal decrease of the LV dimensions in the presence of RV dilation 
No right ventricular failure 
No cardiac tamponade 
Weaning study results
After a weaning study, the treating clinician should be informed to discuss the outcome with the cardiology / cardiothoracic team.
If the weaning study is successful, decannulation should occur within 24 hours. If the weaning study is performed in the morning, the patient will be booked for decannulation later that day. If the weaning study is performed in the afternoon, the decannulation will occur the following morning.
Whilst awaiting theatre time for decannulation (i.e. overnight), consider managing the patient on partial ECMO support (e.g. 1.5-2.0 L/min flow) to further test the patient’s suitability for decannulation. If evidence of worsening heart failure develops, increase ECMO flow and repeat weaning study at a later stage.
If the patient is deemed unsuitable to be separated from ECMO support, multidisciplinary team discussion should be held to further optimise patient condition. Consider repeating weaning study in the next 48 hours.
If the patient has poor prospect of being weaned from ECMO support, multidisciplinary team discussion should take place to consider alternative pathways.
The final stage of the weaning process occurs in the operating theatre where the patient is well anti-coagulated and the ECMO circuit is clamped for a period of time and the patient is observed. The ECMO flow is recirculated after the cannulae are heparin locked and the patient is observed for a period of time. If there is any doubt about successful liberation, this should be discussed with the treating Intensivist.
In addition patients may need vascular procedures like femoral artery patch repair and embolectomy following decannulation. For patients who have subclavian artery return cannulae, decannulation can be done in ICU by cardiothoracic surgeons.
The circuit should be disposed of in a biohazard bag/bin with cytotoxic precautions where appropriate. Re-usable (metal) ECMO Clamps MUST not be discarded.
Returning blood held within the ECMO circuit to the patient prior to cannula removal carries additional risk of air and thrombus entering the patient’s circulation and volume overload. It should only be performed if there is a clinical imperative to conserve blood (e.g. Jehovah’s Witness patient) and warrants prior discussion with the ECMO consultant.
Post decannulation care
Limb perfusion should be monitored during the post-operative period as the patients may develop limb ischaemia in ICU following this procedure. One hourly vascular observations are performed for 12 hours. Vascular surgery team should be notified immediately if limb ischaemia is suspectedthis happens.
A patient may have been initiated on VA ECMO as a bridge to VAD or as a bridge to decision. Acutely deteriorating patients are preferably managed with VA ECMO initially rather than a VAD directly regardless of the chronicity of their cardiac disease.
Patients with no prior destination who are failing to wean off VAof VA ECMO support should have interdisciplinary discussions about their destination. Options at this point include temporary VAD configurations to allow more time, durable VAD, cardiac transplantation or palliation.
Assessment for VAD suitability are jointly done by CAHF/CTH/ICU. A principle framework is listed below but is not strictly in- or exclusive.
- Certainty about irreversibility of cardiac failure
- Acute organ failure (renal, hepatic) resolving or anticipated to resolve
- Absence of chronic life-limiting non-cardiac disease processes
- Functional status prior to admission
- Patient wishes, ideally involving engagement of awake patients in discussion
- Physical and mental ability to operate VAD, family support